Information playback systems frequently utilize a stylus for reading signals from the surface of an information record, typically a plastic disc, that contains stored video and audio information. In some systems the information record has a fine spiral groove to guide the tip of a stylus that contains a thin electrode. In these systems, the stylus is made of a material having sufficient hardness to withstand the abrasion oaused from tracking the groove. Materials which possess such hardness, for example, diamond, generally have a crystallographic structure which presents surfaces exhibiting different qualities depending upon which crystallographic planes the surfaces are oriented along. Consequently, in manufacturing styli from these crystallographic materials for use in video disc playback systems, it is important to know and maintain the orientation of the stylus during the various processing steps in order to achieve uniform styli of high quality.
The stylus is typically fabricated from a relatively small stone, e.g., a diamond stone, which is supported in a holder during the processing steps. The orientation of the stylus is usually controlled during processing by a positioning ring attached to the holder. The holder is adapted to rotate the tip, with respect to the positioning ring, about an axis, so that a particular surface of the tip may be oriented along a desired plane.
U.S. patent application, Ser. No. 189,350, filed Sept. 22, 1980, describes a fixture for holding and orienting a workpiece, such as a stylus, to a desired alignment. A surface of the workpiece is oriented to a reference surface by reflecting light from the workpiece surface to a calibration screen. The present invention provides a novel method and apparatus for aligning two surfaces of the workpiece with respect to the positioning ring within an accuracy of about .+-.1/2.degree.. The two surfaces form the prow of a video disc playback stylus.